{ca,text}: Fix from_issuer_subject_key_identifier usage.

Resolve deprecation warnings in tests:
caucase/ca.py:548: CryptographyDeprecationWarning: Extension objects are deprecated as arguments to from_issuer_subject_key_identifier and support will be removed soon. Please migrate to passing a SubjectKeyIdentifier directly.
  critical=False,
caucase/ca.py:326: CryptographyDeprecationWarning: Extension objects are deprecated as arguments to from_issuer_subject_key_identifier and support will be removed soon. Please migrate to passing a SubjectKeyIdentifier directly.
  x509.SubjectKeyIdentifier,
caucase/test.py:422: CryptographyDeprecationWarning: Extension objects are deprecated as arguments to from_issuer_subject_key_identifier and support will be removed soon. Please migrate to passing a SubjectKeyIdentifier directly.
  critical=False,

caucase/ca.py

@@ -324,7 +324,7 @@ class CertificateAuthority(object):
           x509.AuthorityKeyIdentifier.from_issuer_subject_key_identifier(
             ca_crt.extensions.get_extension_for_class(
               x509.SubjectKeyIdentifier,
-            ),
+            ).value,
           ),
           critical=False, # "MUST mark this extension as non-critical"
         ),
@@ -523,9 +523,6 @@ class CertificateAuthority(object):
             ),
           ] + self._ca_extension_list
         public_key = private_key.public_key()
-        subject_key_identifier = x509.SubjectKeyIdentifier.from_public_key(
-          public_key,
-        )
         now = datetime.datetime.utcnow()
         crt_builder = x509.CertificateBuilder(
           subject_name=subject,
@@ -536,18 +533,11 @@ class CertificateAuthority(object):
           public_key=public_key,
           extensions=[
             Extension(
-              subject_key_identifier,
+              x509.SubjectKeyIdentifier.from_public_key(public_key),
               critical=False, # "MUST mark this extension as non-critical"
             ),
             Extension(
-              x509.AuthorityKeyIdentifier.from_issuer_subject_key_identifier(
-                # Dummy extension, from_issuer_subject_key_identifier accesses
-                # .data directly
-                Extension(
-                  subject_key_identifier,
-                  critical=False,
-                ),
-              ),
+              x509.AuthorityKeyIdentifier.from_issuer_public_key(public_key),
               critical=False, # "MUST mark this extension as non-critical"
             ),
           ],

caucase/test.py

@@ -397,9 +397,6 @@ class CaucaseTest(unittest.TestCase):
       ),
     ])
     public_key = private_key.public_key()
-    subject_key_identifier = x509.SubjectKeyIdentifier.from_public_key(
-      public_key,
-    )
     return private_key, x509.CertificateBuilder(
       subject_name=subject,
       issuer_name=subject,
@@ -409,18 +406,11 @@ class CaucaseTest(unittest.TestCase):
       public_key=public_key,
       extensions=[
         Extension(
-          subject_key_identifier,
+          x509.SubjectKeyIdentifier.from_public_key(public_key),
           critical=False, # "MUST mark this extension as non-critical"
         ),
         Extension(
-          x509.AuthorityKeyIdentifier.from_issuer_subject_key_identifier(
-            # Dummy extension, from_issuer_subject_key_identifier accesses
-            # .data directly
-            Extension(
-              subject_key_identifier,
-              critical=False,
-            ),
-          ),
+          x509.AuthorityKeyIdentifier.from_issuer_public_key(public_key),
           critical=False, # "MUST mark this extension as non-critical"
         ),
         Extension(